Light emitting diodes (LEDs) are a type of semiconductor device that emit a visible light when biased in the forward direction. Lamps incorporating such LEDs as their light source are referred to as LED lamps. Due to their construction, LED lamps are typically smaller than standard bulb or filament type lamps, making their use particularly desirable in applications where a premium is placed on space, such as cameras, watches, computers, computer printers and numerous other compact devices. Additionally, the LED is energy efficient in that it only requires a small amount of electricity in order to generate a relatively strong light. Therefore, the LED is a particularly desirable lighting source in applications where energy efficiency is important, such as with battery powered portable devices.
Generally speaking, although LED lamps offer a relatively high degree of illumination for their size, LED lamps must usually be combined with other LED lamps in order to achieve the same degree of illumination as a light assembly illuminated by standard bulb type lamps. However, the combination of LED lamps typically occupy less space and require less energy to operate than that of the standard bulb type lamps they replace. The space saving and energy efficient features of the LED make it a popular choice with designers and manufacturers who are motivated to reduce the size and/or increase the efficiency of the light source used in their products.
Recently, LED lamps have found application in the automobile industry as a source of illumination, replacing standard bulb type lamps, for exterior lights, such as parking lights, brake lights and the like. It is highly desirable that the light source used in the automobile be energy efficient. The LED is a popular choice in such an application because its use permits the replacement of standard bulb type lamps that require a larger space and consume a greater amount of energy to operate. The space savings that results from replacing standard bulb type lamps with the LED in such an application may be better put to use in the form of added passenger or storage capacity. Size savings can translate into weight savings as well, an important factor in fuel economy.
The standard bulb type lamps are known to have a high rate of failure when used in an automotive application. The high failure rate is attributable to the filament breaking due to sudden shocks or bumps experienced under normal driving conditions. Unlike standard bulb type lamps, LED lamps are immune to such failures due to their inherent construction. The light emitted by an LED is caused by the generation of photons from materials within the LED and is not the product of an electrical current passing through an illuminating filament. Since the LED does not rely on the fragile filament scheme used in bulb type lamps it is better suited for use as a reliable automobile lighting source.
Additionally, standard bulb type lamps are known to generate a large amount of heat during their operation. The heat generated by standard bulb type lamps not only shortens the life of the light source but may cause thermal damage, deformation, cracking or the like to other nearby lighting elements, such as the deformation or cracking of a nearby plastic lens and the like.
Accordingly, the choice of using LED lamps to replace standard bulb type lamps as the lighting source for the automobile is desirable because their use provides a more efficient use of space, is energy efficient, eliminates a common cause of light source failure, and eliminates lens deformation associated with a high heat generating bulb type light source.
A single LED typically produces less illumination than that of a standard bulb type light. Therefore, a plurality of LED lamps are combined in order to provide the same degree of illumination provided by one or more standard bulb lamps. The LED lamps are combined to form a LED module that comprises a plurality of LED lamps and means for mechanically and electrically connecting the LED lamps to a light assembly. The LED module may be configured so that it contains the required number of LED lamps arranged in a circuit to provide the desired degree of illumination. Additionally, the LED module should be configured to accommodate the particular shape or size of the light assembly, which may be defined by the shape or contour of the automobile body design.
LED modules comprising a plurality of LED lamps are known in the art. Such modules are generally made up of a plurality of LED lamps, each having an anode and cathode lead, and a printed circuit board with conductive paths. The plurality of LED lamps are each connected to the printed circuit board by soldering the anode lead of each LED to one path and soldering the cathode lead of each LED to another path. The LED lamps may be arranged along the printed circuit board as desired in order to meet the illumination, space, and configuration requirements of the particular light assembly. The LED module is mechanically attached to the light assembly and the printed circuit board is electrically connected to an anode or cathode electrical source within the light assembly.
Such LED modules typically use a solder connection to connect the anode and cathode lead of each LED to the respective conductive paths in order to ensure a good electrical and mechanical connection. However, solder connecting each LED is a known cause of LED failure. During the soldering operation heat is transferred from the soldering site, through the lead of each LED and to the LED chip resulting in thermal damage. This potential for thermal damage during the manufacture of the LED module may reduce the reliability of the LED and limits its viability as a desirable lighting source.
LED modules known in the art have attempted to minimize the potential for thermal damage to the LED lamps by constructing the LED leads from materials having a low thermal conductivity, such as steel. Using materials of low thermal conductivity reduces the amount of heat that can be transferred from the solder site to the LED chip itself. However, materials having low thermal conductivity necessarily have a correspondingly low electrical conductivity. Therefore, the methods used in the art to minimize the thermal damage of the LED lamps during the soldering operation has resulted in the construction of a LED module that does not display optimal electrical efficiency. Additionally, LED leads constructed from such low thermal conductivity materials effectively limit the amount of power that the LED can dissipate and remain within reliable operational parameters.
Mounting LED lamps on a printed circuit board is also costly. Each LED must be individually positioned on the board for assembly. The boards themselves are costly. Accordingly, a different approach for connecting LED lamps is desirable for both reducing the cost of an LED module and increasing the electrical efficiency of an LED module.
It is, therefore, desirable to have an LED module that can accommodate a plurality of LED lamps in a manner that will optimize the reliability of each LED. It is desirable that mounting of LED lamps in the LED module promotes optimal electrical and thermal efficiency. It is desirable that the LED module permits arbitrary spacing of each LED in order to correspond to predetermined shapes or illumination requirements. It is also desirable that the LED module be practical to produce from both an economic and manufacturing standpoint.